The present invention relates to a modulation analyzing apparatus. In particular, the present invention relates to a modulation analyzing apparatus for performing modulation analysis at terminals of a variety of communication systems in which a mobile communication system is employed as a typical example.
One method of evaluating characteristics of terminals in a mobile communication system includes modulation analysis caused by IQ input.
This analysis is associated with device evaluation of a modulation/demodulation IC incorporated in a hand-held telephone, for example. The analysis is important in the manufacture and inspection of equipment and device that configure a communication system as well as a terminal.
A conventional example of such a modulation analyzing apparatus will be described with reference to FIG. 3 and FIG. 4.
In FIG. 3, reference numeral 10 denotes a radio (hand-held telephone) of a mobile communication system, for example, employed as a sample machine.
This radio (hand-held telephone) 10 comprises a base band section 10A, a quadrature modulating section 10B, a frequency converting section 10C and the like.
Some functions of these sections are achieved by a modulation/demodulation IC (not shown).
From a modulation analyzing apparatus main body 20, there is derived a measurement cable 20 having at its end a probe 20B for receiving an in-phase component I and a quadrature component Q of a base band (modulation) signal from the base band section 10A of the radio (hand-held telephone) 10.
A display section 20C and an operating section 20D or the like are provided at this modulation analyzing apparatus main body 20.
As shown in FIG. 4, the in-phase component I and quadrature component Q of a modulation signal for the quadrature modulating section 10B of the radio (hand-held telephone) 10 are subject to analysis processing through an amplifier 22 and an analog/digital converter (ADC) 23 provided in the modulation analyzing apparatus main body 20.
A modulation signal of a radio that is the sample machine is generally in accordance with an imbalance transmission format.
However, recently, as an IC of the low operation voltage type is fabricated, there is introduced a radio handling a modulation signal of balance transmission format.
In the case where modulation analysis of a radio for a modulation signal of balance transmission format is performed by a modulation analyzing apparatus described above, it is necessary to install a balance/imbalance converter at an input stage of the modulation analyzing apparatus.
Thus, in the conventional modulation analyzing apparatus described above, it is required to mount or remove a balance/imbalance converter according to whether the sample machine is of a balance transmission format or an imbalance transmission format. Because of this, there has been a problem that a communication system including the sample machine cannot be evaluated smoothly.
It is an object of the present invention to provide a modulation analyzing apparatus capable of performing modulation analysis simply irrespective of whether a modulation signal handled by the sample machine is of a balance transmission format or an imbalance transmission format.
According to one aspect of the present invention, there is provided a modulation analyzing apparatus comprising:
a pair of signal lines (32A and 32B) for capturing an inversion in-phase component and a non-inversion in-phase component of a modulation signal inputted to a quadrature modulating section of a sample machine and an inversion quadrature component and a non-inversion quadrature component of the modulation signal;
computers, including adders (34A and 34B), for computing each of the inversion in-phase component and non-inversion in-phase component of the modulation signal and each of the inversion quadrature component and non-inversion quadrature component of the modulation signal, from the pair of signal lines;
analog/digital converting sections (35A and 35B) for analog/digital converting outputs of the computer, respectively;
a waveform storage memory (36) for storing outputs of the analog/digital converting sections, respectively;
a modulation characteristics analyzing section (37) for reading out storage data from the waveform storage memory, and performing predetermined computation processing, thereby analyzing modulation characteristics of a modulation signal inputted to a quadrature modulating section of the sample machine;
a display section (38) for displaying the analysis result caused by the modulation characteristic analyzing section;
balance/imbalance switching sections (43A and 43B) provided at one of the pair of signal lines, the balance/imbalance switching sections grounding the signal lines, thereby switching a state for transmitting a modulation signal of balance transmission format into a state for transmitting a modulation signal of imbalance transmission format.
According to a modulation analyzing apparatus of the present invention, irrespective of whether an IQ input sample machine is of a balance transmission format or an imbalance transmission format, a measurer makes switching operation of a balance/imbalance switching sections (43A and 43B), whereby a signal line for capturing an in-phase component and a quadrature component of a modulation signal can be of balance or imbalance transmission format. Thus, the in-phase component and quadrature component of a modulation signal is directly captured to enable modulation analysis without mounting and removing the balance/imbalance converter. Hence, a communication system can be evaluated smoothly.